Ambient drying to fabricate polybenzoxazine aerogels for thermal insulation in aerospace

Abstract

Polybenzoxazine (PBz) aerogels are promising high-performance, halogen-free flame-retardant thermal insulation materials in aerospace applications. But their widespread use is hindered by high costs, significant drying shrinkage, and poor machinability. Herein, we successfully addressed these challenges by developing PBz aerogel composites using a cost-effective ambient pressure drying method that reduces energy consumption and shortening the preparation cycle. This approach expands the range of available monomers, reduces the inherent rigidity of the network structure, and enhances processability. The resulting PBz aerogels demonstrate low drying shrinkage (as low as 5.68 %), lightweight properties (lowest to 0.322 g cm⁻³), excellent fire-retardant (self-extinguishing in 1.8 s), and exceptional thermal insulation performance (as low as 0.0402 W m⁻¹ K⁻¹ at room temperature and normal pressure). Further studies under various pressures show that at an atmospheric pressure of 10 Pa, the thermal conductivity at room temperature can reach as low as 0.027 W m⁻¹ K⁻¹. Moreover, cryogenic treatment at −196 °C significantly enhances the compressive properties of PBz aerogels without inducing any noticeable shrinkage. Notably, PBz aerogels exhibit outstanding flame resistance, rated as nonflammable rating in vertical burning tests (UL-94, V-1 class), and showing a limiting oxygen index (LOI) as high as 33.7 %. Overall, these remarkable features underscore the exceptional potential of PBz aerogels as advanced thermal insulation materials in the aerospace industry.